1. Field of the Invention
The present invention relates to a digital data processing circuit.
2. Description of the Related Art
In recent years, music data saved in a portable music reproducing device etc. is transmitted by, for example, an FM (Frequency Modulation) transmitter circuit to a car stereo and is reproduced at the car stereo (see, e.g., Japanese Patent Application Laid-Open Publication No. 2006-262521 or No. 2007-88657). FIG. 5 depicts a general configuration of a transmitter-receiver apparatus 200 which includes an FM transmitting device 300 that transmits an audio signal from a portable music reproducing device 310, and an FM receiving device 400 equipped in a car stereo. The FM transmitting device 300 is the device that generates a carrier wave having a frequency corresponding to a result of operation of a controller 320 and that modulates the carrier wave with an audio signal from the portable music reproducing device 310 to output the modulated carrier wave as an FM signal to an antenna 330. The FM receiving device 400 is the device that demodulates an FM signal having a frequency set by a controller 420 among FM signals received by an antenna 410 to reproduce the demodulated signal on a speaker 430 of the car stereo.
When using the transmitter-receiver apparatus 200, a user must first determine a frequency used for transmission and reception in the transmitter-receiver apparatus 200 in consideration of frequencies of FM radio broadcasting etc. used in the surroundings. The user then operates the controller 320 and the controller 420 to enable the transmitter-receiver apparatus 200 to transmit and receive a signal having the determined frequency. As a result, the speaker 430 is able to reproduce an audio signal from the music reproducing device 310.
In the use of the transmitter-receiver apparatus 200, for example, when a reproduced sound from the car stereo is affected by FM radio broadcasting as a result of a change in the surrounding environment, a frequency of an FM signal transmitted and received by the transmitter-receiver apparatus 200 must to be changed. In such a case, the user needs to operate both controller 320 that sets a frequency of a carrier wave from the transmitting device 300, i.e., a transmitting frequency, and controller 420 that sets a receiving frequency of the receiving device 400. There is a problem in that this operation is troublesome to the user.